The invention relates to improvements in apparatus for treating running webs of paper, plastic material or the like. More particularly, the invention relates to improvements in apparatus which can be utilized to remove substances which are entrained by running webs by resorting to a gaseous fluid, particularly to remove films and/or droplets of moisture from freshly exposed and developed webs of photographic paper.
Published German patent application No. 20 56 571 discloses a demoisturizing apparatus wherein the moisture-carrying web is trained over a guide roll and advances past a nozzle which discharges a stream of compressed air.
Published German patent application No. 21 50 796 discloses an apparatus wherein a flattened portion of the moisture-carrying web is caused to advance past an air discharging nozzle. The orifice of the nozzle is located in a plate which is adjacent and parallel to the flattened portion of the running web. In order to enhance and optimize the demoisturizing action of air which issues from the nozzle, the width of the gap between the path of the flattened portion of the web and the plate for the orifice of the nozzle must be reduced to a minimum. If the web consists of exposed and freshly developed photographic paper, the pressure of air which is discharged by the orifice in the plate cannot exceed a certain maximum permissible value because any further rise of air pressure could entail damage to images on the exposed and developed web of photographic paper. On the other hand, if the width of the gap is increased above the minimum acceptable value while the pressure of air is maintained at a maximum permissible value, the velocity of air which reaches the adjacent surface of the running web is too low so that air merely shifts but does not disperse the liquid film on the running web. Atomization of the liquid film, and hence actual drying of photographic paper, takes place only when the width of the gap is maintained at an optimum value. Such width is less than is necessary to permit passage of spliced (overlapping) portions of successive webs of photographic paper and/or to permit passage of customary clamps which are used to separably couple the leaders of webs of photographic paper to entraining bands. Reference may be had to commonly owned U.S. Pat. No. 4,773,580 to Schweiger.